The present application relates generally to an improved data processing apparatus and method and more specifically to an apparatus and method for performing characterization of long range variability in integrated circuit fabrication.
Variability in manufacturing significantly affects cost and quality of a product. More particularly, in the fabrication of integrated circuit (IC) devices, as components become smaller and denser, variability in manufacturing may dramatically reduce the yield of a product. That is, variability in manufacturing may cause a percentage of devices to fail in actual usage or the testing phase when components do not perform as they were designed.
One type of variability is random dopant fluctuation (RDF). Random dopant fluctuation is a form of process variation resulting from variation in the implanted impurity concentration. In metal oxide semiconductor field effect transistors (MOSFET), for example, RDF in the channel region can alter the transistor's properties, especially threshold voltage. In newer process technologies, RDF has a larger effect because the total number of dopants is fewer, and the addition or deletion of a few impurity atoms can significantly alter transistor properties. RDF is a local form of process variation, meaning that two juxtaposed transistors may have significantly different dopant concentrations.
Layout dependent systematic variation has a long range effect. That is, the shapes of components in an integrated circuit may have variation effects over a larger portion of the product. Some forms of long range variability may include rapid thermal annealing (RTA) effects and polycrystalline (PC) silicon perimeter density effects. Rapid thermal processing (RTP) refers to a semiconductor manufacturing process that heats silicon wafers to high temperatures on a timescale of several seconds or less. During cooling, wafer temperatures must be brought down slowly so they do not break due to thermal shock. Rapid thermal annealing (RTA) is a subset of rapid thermal processing. RTA is a process used in semiconductor device fabrication that consists of heating a single wafer at a time in order to affect its electrical properties. Unique heat treatments are designed for different effects.
Long range variability has a longer radius of influence (ROI) and is more difficult to characterize. Long range variability, such as RTA effects and PC perimeter density effects, may account for 20-30% of total front-end-of-the-line (FEOL) variation. FEOL denotes the first portion of integrated circuit fabrication where the individual devices (e.g., transistors, resistors, etc.) are patterned in the semiconductor. FEOL generally covers everything up to, but not including, the deposition of metal layers.